Sterile medical liquids are frequently supplied by manufacturers to hospitals in sterilized bottles. One type of bottle used for the medical liquids is termed a "pouring" container. This container has a wide mouth of approximately 1 inch (2.54 cm) diameter. Thus a physician can quickly pour the sterile liquid into a surgical wound for a flushing action.
An extremely critical area of these "pouring" containers is the closure system. The closure must reliably maintain the sterile nature of the liquid in the bottle and also be easy to open.
In the past, pouring containers included glass type bottles with double closures. The double closure had an inner metal screw cap with a resilient liner or gasket engaging the glass bottle. An outer closure secured over the inner screw cap formed an additional sterility barrier. One of the problems with such a closure was that the gasket of the inner screw cap would not always compress to the same extent. This caused some closures to be very difficult to manually unscrew. One can readily appreciate such a problem by considering the difficulty of opening some glass food jars with metal screw caps and gaskets.